1. Field of the Invention
This invention relates to an improved process for purifying a waste stream. More particularly, this invention relates to the purification of an aqueous waste stream from a tanning process containing ammonia, sulfides, and dissolved organic materials by adsorption on an adsorbent comprising a mixture of alumina and Y zeolite.
2. Description of the Related Art
Waste streams from tanning processes usually contain ammonia, sulfides, and dissolved organics due to the use of chemicals such as NH.sub.4 Cl or (NH.sub.4).sub.2 SO.sub.4 which are used in the tanning of hides and the organic residues from the hides.
Current commercially practiced methods for purifying waste streams from such processes employ precipitation techniques which are expensive and technically unsatisfactory. It is also known to individually remove some of the impurities found in such streams by use of adsorbents such as silica gel, activated alumina or zeolites.
For example, Iwamoto U.S. Pat. No. 4,290,895 describes the removal of ammonia from sewage using silica gel as an adsorbent, while Iwaisako et al U.S. Pat. No. 4,414,111 describes the adsorption of ammonia from an aqueous solution using a composite adsorbent having a skin-core structure comprising a mixture of a powdery ion-exchange type adsorbent such as a natural or synthetic zeolite and an acrylonitrile polymer.
The use of an activated alumina adsorbent to separate various neutral organic substances for layer chromatographical purposes is described in Matayasi et al U.S. Pat. No. 4,225,639. Bernhardt et al in an article entitled "Anwendung der Aktivtonerdefiltration zur Eliminierung von Phosphaten aus kleinen Talsperrenzulaufen" published in Zeitschrift fur Wasser und Abwasser Forshung, Volume 14, 1981, at pages 180-187, describes the results obtained from the treatment of effluents from fish farming ponds with activated alumina. The authors claim an 80% reduction in phosphates but state that reductions in ammonium levels and total organic carbons were much more variable.
The use of alumina to remove ammonium nitrogen and organics from waste water is also discussed by Starkey, Jr. et al in report EPA-660/3-74-022 (August 1973) entitled "An Investigation Of Ion Removal From Water And Wastewater", prepared for the U.S. Environmental Protection Agency. The authors describe the alumina adsorption column on page 28 of the report and show carbon and ammonia nitrogen removal results in Table 8.
Culp et al in the "Handbook of Advanced Wastewater Treatment", 2nd Edition, published by Van Nostrand Reinhold Company, N.Y. in 1978, describe nitrogen removal in chapter 7. From pages 323 to 348, the authors describe the use of selective ion exchange to remove ammonium nitrogen using clinoptilolite, a naturally occurring zeolite.
However, it has been found that the use of either conventional activated alumina or a zeolite alone will not provide the desired amount of simultaneous removal of ammonia, sulfides, and organic materials from wastewaters from a tanning process.